Fair bits     Sun, 07 Mar 2010 17:10 Cygnum writes: You're given a black box that produces random bits. It produces '1' with a constant probability p and '0' with a constant probability probability 1-p (the bits are independent). You need  to come up with a system that uses that black box but produces fair independent random bits i.e. '1' with probability 0.5 and '0' with probability 0.5. P is of course unknown, but constant. Note - The given black box is your only way to produce random numbers. read comments(11) / write comment / 476 views

Suntop Stickers     Tue, 02 Mar 2010 19:33 Data writes: Your school going kid is a fan of the SunTop drink. Each drink packet consists of a SunTop sticker which should be peeled off from the packet and collected. Say, that in all there are 52 unique SunTop stickers and each SunTop drink packet costs 1 Saudi Riyal. Give an estimate of the total money that you would have to spend on your kid to collect all the 52 unique SunTop stickers. I.e Estimate the number of SunTop drinks you have to buy inorder to get all the 52 unique SunTop stickers. Note: You get exactly one SunTop sticker per Suntop drink packet. You also cannot exchange stickers with other kids. The buying process is random. I.e. you have to take whatever SunTop packet the store owner gives you. You donot have the choice to pick the drink on your own. read comments(12) / write comment / 685 views

Sat-nav systems under growing threat from 'jammers'     Thu, 25 Feb 2010 09:26 Data writes: Technology that depends on satellite-navigation signals is increasingly threatened by attack from widely available equipment, experts say. While "jamming" sat-nav equipment with noise signals is on the rise, more sophisticated methods allow hackers even to program what receivers display. News Editor Note: The impacts are significant. read comments(6) / write comment / 521 views

Jaywalking     Mon, 22 Feb 2010 11:50 Data writes: You have been caught jaywalking. The officer gives you two options- one day in prison or a $100 fine. You, being the smart guy asks for a third option. The officer being a math buff thinks for a while,goes back into his vehicle and picks a complete set of chess pieces (16 white and 16 black) and two empty boxes. He asks you to place the chess pieces in the two boxes, the only constraint is that all the pieces should be placed. He then asks you to close your eyes and the officer changes the order of the box(not its contents) randomly. Now, again with your eyes closed you are asked to pick a piece from one of the two boxes. - If it is a white piece that you picked, you are free to go without any fine - If it is a black piece that you picked, you are at the officer's mercy. What is your best strategy in placing the chess pieces in the empty boxes so that you have the highest probability of picking a white piece? read comments(15) / write comment / 1116 views

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